Analysis of Flexible Pavement Using IIT PAVE software

RITESH KUMAR (2000970009020)
SABOOR KHAN (2000970009021)
SAURABH KUMAR (2000970009024)
PRABHAT (2000970009015)
DIGVIJAY YADAV (2000970009010)
Presented By
Project Guide
Mr. ARUN KUMAR
Analysis of Flexible Pavement using
IIT-PAVE Software
Department Of Civil Engineering

OBJECTIVE
 Analysis of stresses, strains and deflections caused at different critical locations in a
pavement by a uniformly distributed single load applied over a circular contact area at
the surface of the pavement can be computed using IIT PAVE software.
 Design and analysis of Overlays for Strengthening of Weak Pavements.
 Analysis of the flexible or bitumen pavement using IRC: 37-2018 guidelines.

IIT PAVE
IITPAVE software, which is an updated version of FPAVE developed for
MoRTH Research Scheme R-56 “Analytical design of Flexible Pavement”, has been used
for the analysis of linear elastic layered pavement system. This is a multilayer analysis
programme used for design, analysis of the flexible or bitumen pavement using IRC: 37-
2018 guidelines. In this software we enter thickness of pavement layers, loads applied over
the surface of pavement, tire pressure, spacing between the wheels and Poisson´s ratio as
inputs. After running the software actual horizontal tensile strain and vertical compressive
strains at critical locations of the pavement are obtained as output.

METHODOLOGY
 Mechanistic-Empirical Method:
Performance is explained in term of
mechanistic empirical parameter such as
Stress, Strains and Deflection calculated
by using linear elastic layered theory.
Vertical strain on top of subgrade
( 𝜀𝑉 ) considered to be causative
factor for permanent deformation in
subgrade.
Horizontal tensile strain (𝜀𝑡) at the
bottom of the bituminous bound
layer is an indicator for fatigue
cracking in bituminous layer
Pavement Section with Bituminous Layer(s),
Granular Base and GSB Showing the
Locations of Critical Strains

 Pavement is modelled as multilayer System:
The bottom most layer
(subgrade) is considered to be semi-infinite, and all the upper layers are assumed to be
infinite in the horizontal extent and finite in thickness.

Failure In Flexible Pavement
1. Rutting in Bituminous Pavements :
Rutting is the longitudinal depression in the wheel
path in bituminous pavements, which can be attributed to excessive consolidation, formed
by an accumulation of permanent deformations caused by repeated heavy loads, or lateral
movement of the material, caused by shear failure of the bituminous concrete layer, or a
combination of both mechanisms.

Rutting in pavement occurs :
a) Due to deformation in subgrade and other unbound layers (granular sub-base and base)
b) Due to rutting in bituminous layer.
c) Due to Climate and environment are other factors also.
Bituminous Layer

2.Fatigue cracking flexible pavement:
• Fatigue crack is a main form of structural damage in flexible pavements. Under the
action of repeated vehicular loading, deterioration of the asphalt concrete materials in
pavements, caused by the accumulation and growth of micro and macro cracks,
gradually takes place.
• Improper drainage design for pavement.
• Poor construction of pavement, i.e., inadequate compaction and subgrade preparation

PROCEDURE
a. Click on Design New Pavement Section to give inputs for the analysis of the
selected pavement section.

The inputs to be entered are:
(i) Number of pavement layers including subgrade (if all the bituminous layers are taken as
one bituminous layer and all the granular layers are taken as one layer, then the number
of layers is 3 (bituminous layer, granular layer and subgrade).
(ii) Resilient modulus/Elastic modulus values of all the layers in MPa
(iii) Poisson’s ratio values of all the layers
(iv) Thicknesses (in mm) of all the layers except subgrade.

Resilient modulus/Elastic modulus :-
The resilient modulus (Mr) is the elastic modulus
based on the recoverable strain under repeated loads. The resilient modulus of soils can be
determined in the laboratory by conducting the repeated tri-axial test as per the procedure
detailed in AASHTO T307-99[19]. Since these equipment are usually expensive, the
following relationships may be used to estimate the resilient modulus of subgrade soil (MRS)
from its CBR value.
MRS = 10.0 * CBR for CBR ≤ 5 % (6.1)
MRS = 17.6 * (𝐶𝐵𝑅)0.64 for CBR > 5 % (6.2)
Where,
MRS = Resilient modulus of subgrade soil (in MPa).
CBR = California bearing ratio of subgrade soil (%)
Resilient modulus of the granular layer
𝐌𝐑𝐆𝐑𝐀𝐍 = 𝟎. 𝟐. (𝐇)𝟎.𝟒𝟓. 𝐌𝐑𝐒𝐔𝐏𝐏𝐎𝐑𝐓
Where,
H = Thickness of granular layer in mm
MRGRAN = Resilient modulus of the granular layer (MPa)
MRSUPPORT = (Effective) resilient modulus of the supporting layer (MPa)

Material Type Elastic/Resilient Modulus (MPa)
Poisson’s
Ratio
Bituminous layer with VG40 or
Modified Bitumen
3000 or tested value (whichever is
less)
0.35
Bituminous layer with VG30 2000 or tested value (whichever is
less)
0.35
Cement treated base 5000 0.25
Cold recycled base 800 0.35
Granular interlayer 450 0.35
Cement treated sub-base 600 0.25
Unbound granular layers 𝐌𝐑𝐆𝐑𝐀𝐍 = 𝟎. 𝟐. (𝐇)𝟎.𝟒𝟓
. 𝐌𝐑𝐒𝐔𝐏𝐏𝐎𝐑𝐓 0.35
Unbound granular base over
CTSBsub-base
300 for natural gravel
350 for crushed aggregates
0.35
0.35
Subgrade MRS = 10.0 * CBR for CBR ≤ 5 %
MRS = 17.6 * (𝑪𝑩𝑹)𝟎.𝟔𝟒
for CBR > 5 %
0.35
Recommended Material Properties for Structural Layers
Table 11.1 from IRC-37-2018

Single wheel load:
Analysis is done for a standard axle of 80 KN, a single wheel load of
20000 (N) is given as input. For carrying out cumulative fatigue damage analysis of CTB
layers, the tensile stress/strain at the bottom of the CTB layer has to be calculated for
different axle loads. For this, the IITPAVE will be run with different single wheel loads
corresponding to the axle load considered.
80 KN
40 KN
20 KN 20 KN
40 KN
20 KN 20 KN

Tyre (contact) pressure:
For analysis standard contact pressure of 0.56 MPa is
considered. For analyzing the tensile strain or tensile stress at the bottom of the
CTB base for carrying out fatigue damage analysis of CTB bases using equations
3.5 to 3.7, the contact pressure suggested is 0.80 MPa. The bituminous layer
bottom-up fatigue cracking and subgrade rutting performance models have been
developed/calibrated with the strains calculated with standard axle (80 KN)
loading and a contact pressure of 0.56 MPa and hence, these inputs should not be
changed.
The single vertical load applied at the surface is described in terms of
 Contact pressure and radius of contact area.
OR
 Wheel load and contact pressure.
OR
 Wheel load and radius of contact area.

Analysis Point:
i. The number of locations in the pavement at which stress / strain / deflection
has to be computed. This input can be entered through a drop down menu.
ii. The points that are need to be analyzed must be mentioned.
iii. The depth from top surface to the point to be analyzed for each of the point
must be clearly mentioned in mm
iv. The radial distance(mm) from the center of the dual wheel is considered.
Radial distance = s/2

 After all the inputs are entered, submit them by Clicking on “Submit”.
 To change the data submitted, use “Reset” option.
 After successfully submitting the inputs use the “RUN” options which will
appear next to “Reset” after the inputs are submitted.
 Fig. shows the screenshot of the output page showing the output for the input
data.

Analysis of Flexible Pavement Using IIT PAVE software

Output Data Presented by Sign. :-
Z = Depth of the location measured from pavement surface
R = Radial distance of the location measured from the center of the circular contact
area of the load.
The mechanistic parameters reported in the output page are:
Sigma Z = Vertical stress
Sigma T = Tangential stress
Sigma R = Radial stress
Tao RZ = Shear stress
Disp Z = Vertical deflection
epZ = Vertical strain
epT = Horizontal tangential strain
epR = Horizontal radial strain
Positive(+) stresses and strains are “tensile”
Negative(-) stresses and strains are “Compressive”

TAFFIC DATA OF OTHER DISTRICT ROAD
FROM
PWD BANDA

TRAFFIC CENSUS
From 22-06-2021 To 23-06-2021 WEEKLY TAFFIC SUMMARY Road Classification :: Other District Road
Name Of Work Kamasin - Oran Road Road , Strengthening of Kamasin – Oran Road from 0.00 Kmp to 6.00 Kmp under PWD BANDA
Count Dates
Fast Vehicles Slow Vehicles
Cars, Jeeps,
Vans,
Three
Wheelers
etc.
Buses Trucks
Motor
cycles &
Scooters
Total Fast
Animal
Drawn
Vehicles
Cycles
Rickshaw
Others
(Specify)
Total Slow
Up Down Up Down Up Down Up Down Up Down
Total
col. 10
& 11
Up Down Up Down Up Down Up Down
Total
col. 19
& 20
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21
DAY : 1 124 122 343 338 408 434 154 175 1029 1069 2098 0 0 123 142 92 100 215 242 457
DAY : 2 121 121 490 378 359 287 146 185 1116 971 2087 0 0 167 166 138 134 305 300 605
DAY : 3 124 125 338 309 435 438 164 172 1061 1044 2105 0 0 132 101 96 106 228 207 435
DAY : 4 132 114 418 412 367 337 120 142 1037 1005 2042 0 0 122 109 101 114 223 223 446
DAY : 5 109 110 434 408 364 332 121 141 1028 991 2019 0 0 153 146 112 149 265 295 560
DAY : 6 107 101 418 380 373 346 124 144 1022 971 1993 0 0 146 145 86 208 232 353 585
DAY : 7 96 86 426 405 362 367 124 134 1008 992 2000 0 0 125 126 112 143 237 269 506
Total 813 779 2867 2630 2668 2541 953 1093 7301 7043 14344 0 0 968 935 737 954 1705 1889 3594
7 days average 116 111 410 376 381 363 136 156 1043 1006 2049 0 0 138 134 105 136 244 270 513
Total Up & Down for Vehicle
Type 227 785 744 292 2049 0 272 242 513

Total Numbers of commercial vehicles
P = [ Total no. of Buses in Both Direction + Total no. of Truck ( including Agricultural
Tractor ) in Both Direction ]
= 785 + 744
= 1529 CV/Day
A = 𝐏(𝟏 + 𝐫)𝐱
= 1529 1 + 0.05 2
= 1686 𝐶𝑉/𝐷𝑎𝑦
A = Initial traffic (commercial vehicles per day) in the year of completion of construction
r = Annual growth rate of commercial vehicles in decimal (5% = 0.05)
x = No. of years between the last count and the year of completion of construction = 2

Performance Criteria
NR = 4.1656 x10−8
[1/εv]4.5337 (for 80 % reliability)
NR = 1.4100 x10−8
[1/εv]4.5337 (for 90 % reliability)
Subgrade rutting criteria -
Where,
NR = Subgrade rutting life (cumulative equivalent number of 80 kN standard axle loads
that can be served by the pavement before the critical rut depth of 20 mm or more
occurs).
εv = Vertical compressive strain at the top of the subgrade calculated using linear elastic
layered theory by applying standard axle load at the surface of the selected
pavement system.

Fatigue cracking criteria for bituminous layer
𝑁𝑓 = 0.5162 × 𝐶 × 10−4 ×
1
ε𝑡
3.89
×
1
𝑀𝑅𝑀
.0.854
(for 90 % reliability)
C = 10𝑀
, M= 4.84
V𝑏𝑒
V𝑏𝑒+V𝑎
− 0.69
Va = Per cent volume of air void in the mix used in the bottom bituminous layer
Vbe = Per cent volume of effective bitumen in the mix used in the bottom bituminous layer
Nf = Fatigue life of bituminous layer (cumulative equivalent number of 80 kN standard
axle loads that can be served by the pavement before the critical cracked area of 20
% or more of paved surface area occurs)
Εt = Maximum horizontal tensile strain at the bottom of the bottom bituminous layer
(DBM) calculated using linear elastic layered theory by applying standard axle
load at the surface of the selected pavement system
MRm = Resilient modulus (MPa) of the bituminous mix used in the bottom bituminous
layer, selected as per the recommendations made in these guidelines.

Computed Horizontal Allowable Horizontal
Tensile Strain From < Tensile Strain
IIT Pave
Computed Vertical Allowable Vertical
Compressive Strain < Compressive Strain
From IIT Pave
HENCE
OK
HENCE
OK
Comparison Of Values-

NR= Subgrade rutting life (cumulative equivalent number of 80 kN standard axle loads
that can be served by the pavement before the critical rut depth of 20 mm or more
occurs)
εv = Vertical compressive strain at the top of the subgrade calculated using linear elastic
layered theory by applying standard axle load at the surface of the selected pavement
system

No. of layers 3
E values (MPa) 3000.00 66.60 215.00
Mu values 0.35 0.35 0.35
thicknesses (mm) 180.00 480.00
single wheel load (N) 20000.00
tyre pressure (MPa) 0.56
Dual Wheel
Z R sigmaZ SigmaT SigmaR TaoRZ DispZ epZ epT epR
180.00 0.00 -0.5009E-01 0.8079E+00 0.6632E+00 -0.4731E-02 0.3117E+00 -0.1883E-03 0.1978E-03 0.1327E-03
180.00L 0.00 -0.5009E-01 -0.8438E-02 -0.1165E-01 -0.4732E-02 0.3117E+00 -0.6465E-03 0.1978E-03 0.1327E-03
180.00 155.00 -0.5014E-01 0.7851E+00 0.5362E+00 -0.1267E-01 0.3257E+00 -0.1709E-03 0.2050E-03 0.9299E-04
180.00L 155.00 -0.5014E-01 -0.8971E-02 -0.1450E-01 -0.1267E-01 0.3257E+00 -0.6295E-03 0.2050E-03 0.9299E-04
660.00 0.00 -0.2288E-01 -0.9413E-02 -0.9635E-02 -0.2601E-02 0.1103E+00 -0.2434E-03 0.2954E-04 0.2504E-04
660.00L 0.00 -0.2288E-01 -0.2934E-02 -0.3654E-02 -0.2601E-02 0.1103E+00 -0.9569E-04 0.2955E-04 0.2503E-04
660.00 155.00 -0.2404E-01 -0.9877E-02 -0.1000E-01 -0.3100E-02 0.1127E+00 -0.2565E-03 0.3061E-04 0.2801E-04
660.00L 155.00 -0.2404E-01 -0.3042E-02 -0.3453E-02 -0.3100E-02 0.1127E+00 -0.1012E-03 0.3061E-04 0.2802E-04
Output Data From IIT PAVE Software
Allowable vertical compressive strain on subgrade −
( ε𝑣
) = 0.0003409 < Actual vertical compressive strain
Allowable horizontal tensile strain at the bottom of bituminous layer -
(ε𝑡
) = 0.000172799 < Actual horizontal tensile strain
Trial is Failed

6.4 Effective modulus/CBR for design :
Step-1 Using IITPAVE software, determine the maximum surface deflection (δ) due to
a single wheel load = 1.482 mm [ Min - 1.482 mm , Max- 3.00 mm]
Considering available data for design
a) The Poisson’s ratio value of both the layers (µ) = 0.35
b) Single Wheel Load = 40000 N
Step-2 Using the maximum surface deflection (δ) computed in step-1 above, estimate
the resilient modulus MRS of the equivalent single layer using equation 6.3
M =
𝟐 (𝟏−𝞵𝟐)𝞺𝛼]
𝜹
= 100.00 Mpa Ok. Value is accepted
Where,
MRS = Resilient modulus shall be limited to a maximum value of 100 Mpa. Para -6.4.2

𝑀𝑅𝑆 =
2 1 − 𝜇2 𝑃. 𝑎
𝛿
Where,
p = contact pressure = 0.56 MPa
a = radius of circular contact area, which can be calculated using the load
applied (40,000 N) and the contact pressure ‘p’ (0.56 MPa) = 150.8 mm
μ = Poisson’s ratio
AASHTO - American Association of State Highway and Transportation Officials
(6.3)
Poisson’s ratio value or subgrade soil may be
taken as 0.35. and deflection is calculated by
following equation.

No. of layers 3
E values (MPa) 3000.00 215.00 66.60
Mu values 0.350.350.35
thicknesses (mm) 190.00 480.00
single wheel load (N) 20000.00
tyre pressure (MPa) 0.56
Dual Wheel
Z R SigmaZ SigmaT SigmaR TaoRZ DispZ epZ epT epR
190.00 0.00-0.7442E-01 0.5338E+00 0.4296E+00-0.1186E-01 0.3338E+00-0.1372E-03 0.1365E-03 0.8960E-04
190.00L 0.00-0.7443E-01 0.1051E-02-0.6419E-02-0.1186E-01 0.3338E+00-0.3374E-03 0.1365E-03 0.8960E-04
190.00 155.00-0.7158E-01 0.5109E+00 0.3201E+00-0.3191E-01 0.3428E+00-0.1208E-03 0.1413E-03 0.5545E-04
190.00L 155.00-0.7158E-01 0.8330E-03-0.1284E-01-0.3191E-01 0.3428E+00-0.3134E-03 0.1413E-03 0.5545E-04
670.00 0.00-0.1396E-01 0.2061E-01 0.1867E-01-0.1937E-02 0.2475E+00-0.1289E-03 0.8819E-04 0.7602E-04
670.00L 0.00-0.1396E-01 0.1188E-02 0.5987E-03-0.1937E-02 0.2475E+00-0.2191E-03 0.8807E-04 0.7613E-04
670.00 155.00-0.1468E-01 0.2162E-01 0.2048E-01-0.2345E-02 0.2519E+00-0.1368E-03 0.9111E-04 0.8396E-04
670.00L 155.00-0.1468E-01 0.1240E-02 0.8866E-03-0.2345E-02 0.2519E+00-0.2316E-03 0.9111E-04 0.8396E-04

µ = Poisson’s ratio = 0.35
p = Contact pressure for the above specified load (p)= 0.56 Mpa
α = Radius of circular contact area for this load and contact pressure = 150.80 mm
δ = Obtained maximum surface deflection computed in step-1 above = 1.482 mm
Effective CBR value for above accepted estimated resilient modulus MRS
below equation derived from equation 6.2
CBR =
𝟎.𝟔𝟒 𝑴𝑹𝑺
𝟏𝟕.𝟔
= 15.10% Since the value is > 5% . Hence Ok.

Computed Horizontal Allowable Horizontal
Tensile Strain From < Tensile Strain
IIT Pave
Computed Vertical Allowable Vertical
Compressive Strain < Compressive Strain
From IIT Pave
HENCE
OK
HENCE
OK

Analysis of Flexible Pavement Using IIT PAVE software

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